A joint generally consists of two relatively rigid bony structures that maintain a relationship with each other. Soft tissue structures spanning the bony structures hold the bony structures together and aid in defining the motion of one bony structure relative to the other. In the knee, for example, the bony structures are the tibia and the femur. Soft tissue such as ligaments, tendons, menisci, and capsule provide support to the tibia and femur. A smooth and resilient surface consisting of articular cartilage covers the bony structures. The articular surfaces of the bony structures work in concert with the soft tissue structures to form a mechanism that defines the envelop of motion between the structures. When fully articulated, the motion defines a total envelop of motion between the bony structures. Within a typical envelop of motion, the bony structures move in a predetermined pattern with respect to one another. In the example of the hip joint, the joint is a ball in socket joint that is inherently stable. The capsule and ligaments spanning the hip joint provide stability while the muscles provide motion.
The articular surfaces of the bony structure became damaged by a variety of diseases, accidents, and other causes. A common disorder of joints is degenerative arthritis. Degenerative arthritis causes progressive pain, swelling, and stiffness of the joints. As the arthritis progresses the joint surfaces wear away, resulting in contractures of the surrounding soft tissues that provide stability to the joint. Moreover, progression of the disease process increases pain and reduces mobility.
Treatment of the afflicted articular bone surfaces depends, among other things, upon the severity of the damage to the articular surface and the age and general physical robustness of the patient. Commonly, for advanced arthritis, joint replacement surgery is necessary wherein the articulating elements of the joint are replaced with artificial elements commonly consisting of a part made of metal articulating with a part made of ultra high molecular weight polyethylene (UHMWPE).
A relatively young patient with moderate to severe degeneration of the hip joint is often treated with drug therapies. While drug therapies may temporarily provide relief of pain, progression of the disease, with resulting deformity and reduced function, ultimately necessitates surgery. Alternative treatments such as non-steroidal anti-inflammatory drugs and cortisone injections similarly provide only temporary relief of symptoms.
In severe situations, the entire articular surface of a bone may be replaced with an artificial surface, as, for example, when the acetabular socket and femoral head are replaced with a prosthetic device including an UHMWPE bearing to resurface the acetabulum and a polished metal or ceramic femoral head mounted to a stem extending into the medullary canal of the proximal femur to replace the femoral head. Joint replacement surgery has become a proven and efficacious method of alleviating pain and restoring function of the joint.
Current methods of preparing the rigid elements of a joint to receive components as in joint replacement surgery involve extensive surgical exposure. The exposure must be sufficient to permit the introduction of drills, reamers, broaches and other instruments for cutting or removing cartilage and bone that subsequently is replaced with artificial surfaces. For total hip replacement, the acetabular articular surface and subchondral bone is removed by spherical reamers, the femoral head is resected with an oscillating saw, and the proximal medullary canal is shaped with broaches. A difficulty with total hip replacement is that the invasiveness of the procedure causes significant interoperative blood loss and extensive rehabilitation because muscles and tendons must be released from the proximal femur to mobilize the femur and gain exposure of and access to the acetabular fossa.
Invasiveness. Conventional total hip arthroplasty is indicated for painful arthritis of the hip joint. The procedure involves exposing the hip joint through a large incision to provide the surgeon full visualization of the hip joint and the acetabular region and to provide access for surgical power instruments. In order to appropriately prepare the bony structures of the hip joint, the major muscles spanning the joint are commonly disrupted to gain adequate exposure of the joint. Steps of the procedure include removing the femoral head followed by reaming and broaching the proximal femoral canal to prepare a bony surface to support a hip stem. The stem is implanted and may be cemented in place, or press fit for bony ingrowth. The acetabulum is typically prepared using a hemispherical reamer to remove cartilage down to bleeding bone. Once the acetabulum is prepared, an acetabular component is implanted, either by cementing in place or press fitting for bony ingrowth. Surgical exposure is necessary to accommodate the bulk and geometry of the components as well as the instruments for bone preparation. The surgical exposure, which may be between six and twelve inches in length, may result in extensive trauma to the soft tissues surrounding the hip joint along with the release of muscles that insert into the proximal femur. The surgical exposure increases bleeding, pain, and muscle inhibition; all of which contribute to a longer hospitalization and rehabilitation before the patient can be safely discharged to home or to an intermediate care facility.
The prepared bony surfaces are technically referred to as the acetabular fossa, femoral canal and metaphyseal region of the femur. Prior to placing the final implants into the prepared spaces, a femoral trial, which may be the broach in some systems, is placed in the proximal femur along with a trial femoral head and neck, and an acetabular trial is placed into the acetabulum to facilitate trial range of motion and evaluation of hip stability prior to placement of the final total hip implants.
For patients who require hip replacement it is desirable to provide surgical methods and apparatuses that may be employed to gain surgical access to articulating joint surfaces, to appropriately prepare the bony structures, to provide artificial, e.g., metal or plastic, articular bearing surfaces, and to close the surgical site, all without substantial damage or trauma to associated muscles, ligaments or tendons. To attain this goal, a system and method is needed to enable articulating surfaces of the joints to be appropriately sculpted using minimally invasive apparatuses and procedures.
A system to enable minimally invasive total hip arthroplasty that will minimize soft tissue trauma and accelerate postoperative rehabilitation is needed. Further, because minimally invasive techniques inherently limit observation of the surgical site, compromising visualization of the prepared bony surfaces, a device is also needed for inspection of the prepared bony surfaces. During a surgical procedure, bone debris and blood will gather in the surgical site and require removal from time to time to visualize the acetabulum. After preparation of the acetabulum, an acetabular component is implanted. A variety of acetabular components such as cemented UHMWPE cups, cemented or press fit metal shells with UHMWPE, metal, or ceramic bearing liners are presently used. Typically, placement of a press fit shell requires an impaction force to fully seat the implant into support bone. However, the size and location of the minimally invasive incision may not be optimal for proper orientation and application of force to adequately seat and stabilize an acetabular implant. Thus, an impaction device is needed that allows for impaction of the acetabular component with the hip reduced or articulated for use with a minimally invasive exposure for total hip arthroplasty. It may also be desirable to use a surgical navigation system to position the acetabular implant.